The autistic spectrum (sometimes referred to as the autism spectrum) is a developmental and behavioral syndrome that results from certain combinations of characteristically autistic traits. Although these traits may be normally distributed in the population, some individuals inherit or otherwise manifest more autistic traits. At the severe end of the spectrum is low-functioning autism which has profound impairments in many areas, to Asperger's syndrome, and high-functioning autism, to "normal" behaviour and perhaps hypersocialization on the high end of the spectrum.

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In practice, autistic spectrum disorder and pervasive developmental disorder are synonymous, but making a distinction is valuable. PDD refers to those psychological and behavioral developmental disorders encompassing many areas of functioning: language and communication, self-help skills, motor coordination, executive function, and scholastic achievement. The nosological category of pervasive developmental disorders includes syndromes that may be etiologically unrelated to autism, with autistic-like behavior being only one part of the disorder: Rett's syndrome and childhood disintegrative disorder.

Behaviorally, certain characteristics identify the autism spectrum. The number of autistic traits present determines the severity of autism in the individual. These autistic traits may be beneficial for some disciplines like science, mathematics, engineering, and software. Some autistic individuals might show a marked proficiency in rote memorization which may help learn the foundation of these subjects; however, the exceptionally good aptitude (in these subjects) of high functioning autistic spectrum persons may be due to their ability to readily identify patterns and apply them consistently to new situations outside of established knowledge or teaching. These savant skills, although popularly considered to be a major part of autistic disorders, are evident only in about 5% of autistic individuals (Klin and Volkmar, 1997).

Some research has indicated a possible genetic and behavioral connection between ADHD and autism. As a result, some clinicians have suggested that ADHD be included under the category of autism-spectrum disorders. [1]

Diagnoses of ADHD together with autism spectrum disorder are becoming increasingly common in children. In young children, the two conditions can appear similar. However, as children age, differences emerge between the two conditions. Children with typical autism become more withdrawn, while with a suitable environment hyperactivity reduces. In either event, problems with social skills can develop.

By contrast, children with ADHD rarely calm down with age but often develop social and communication skills to a normal level. Any issues with social skills experienced by children with ADHD may have other causes. Examples include low self-esteem or difficulty with quiet, constructive social interaction.